External Morphology
The mouth is located on the underside of the body and from the anterior end protrudes 20 oral tentacles, which exhibit the characteristic tube feet (Conand, Morel & Mussard 1997). These are used to move particles of sand into the phayrnx. These podia are arranged around the calcareous ring and on average extend approximately to 2.5cm (Conand, Morel & Mussard 1997), allowing individuals to cover a large surface area at a single time during feeding. The body is covered in tube feet, with many reduced to buttons, which look like small spines. These are involved in suction and allow movement across the see floor. The body resembles a long cyclindrical tube and has bilateral symmetry. Sand is excrete from the anus, with small faecal deposits often seen at the rear end of an individual. Ad deposit feeders, H. leucospilota is constantly churning the sand, playing an important role in the carbon cycle.
This species has the ability to deform and manipulate its body, to hide under crevices as well as retract itself when threatened. When disturbed, the mouth and tentacles can be fully retracted into the trunk, making it difficult to distinguish the anterior from the anus. Another defence mechanism is to eject Cuvierian tubules from the anus, which form sticky threads to entangle the predator.
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1. Anterior - Mouth
2. Posterior - Anus
3. Feathery feeding buccal tentacles are used to pick up food and shovel it into the mouth.
4. The calcareous ring can be seen around the outside of the mouth.
5. The oral tube feet extend from around the mouth, leading to the pharynx.
6. Cuvierian tubules are ejected from the posterior end of the individual.
7. The sticky threads are used to entangle predators.
8. The Cuverian tubules have a white colouring and regenerate.
9. Faecal deposits of excreted sediment can often be seen at the rear end of individuals.
10. The anus ejects threads when agitated.
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